onboard.
The current onboard graphics are actually on the chip itself.
So the interaction between the graphics and cpu is totally different to the old - intel - method of having the grahics chip on the motherboard itself.
Totally different ballgame.

But you do have to be careful that you buy an A series cpu as there are no longer video chips on the motherboards :-)

The a8 and a10 give you 4 cpu cores and 6 or 8 graphics cores.
They're good for most modern games let alone cad work.

My 3d printer machine is actually much much cheaper. I'm using a miniitx AM1 board with a really cheap quadcore chip with R3 graphics chip.

haven't found anything to slow it down yet.

What you need to understand is that compared to video games - most cad packages pull hardly any gpu power.
Games are refreshing at a minimum of 30 frames a second with many hundreds of fully rendered - often moving - models.
Unless you're designing an entire jumbo jet in a single file - you'll never come close to using that kind of processing power from a cad program.

So a decent budget system might consist of:
Amd AM1 5350 cpu
128gb ssd
MSI AM1I AMD Mini ITX Motherboard (LAN, VGA, HDMI, DVI)
4 gb 1600mhz ddr3
Any case you fancy that comes with a psu - this thing pulls very little power/
dvd drive if you don't have an external usb one - you'll probably never use the dvd drive, but a usb one is useful for setting up.

If you do what i did and screw the board into a sheet of wood and use a basic full size psu and 64gb ssd. The whole thing comes in at under £100.
Add a nan wireless chip for about £10 and you're good to go :-)
A decent mini itx case won't break the bank ether: http://www.amazon.co.uk/CiT-Mini-ITX...+case+with+psu

So for under £150 you can easily build a decent 3dprinter/cad machine.

Or you can go the other route and go big and really fast. That won't break the bank either.

Computers are really easy to build. The important bit is how you set them up software wise.
I like windows 7.
But you could also go down the linux route. Free and most things - including simplify3d run on it now.

There must be cad packages for linux and they'll most likely be free as well.

Most linux distros can be downloaded and installed from a memory stick these days. So you'll never need a dvd drive :-)